1. Field of the Invention
The present invention relates to an axial elongation measuring method and device for a rotary shaft, such as a gas turbine or steam turbine rotor shaft, that elongates in the axial direction.
2. Description of the Prior Art
Because a rotor shaft of a gas turbine or steam turbine undergoes axial elongation according to temperature changes, it is necessary to accurately monitor whether or not the elongation is within a predetermined range so that no mutual contact of a moving blade and a stationary blade may be caused. One example of the prior art used to measure the axial elongation of a rotary shaft is to use a gap sensor to detect a gap caused by the axial elongation, as shown in FIG. 7.
In FIG. 7, numeral 1 designates a rotary shaft, and this rotary shaft 1 is provided with a target face 2 for measuring the axial elongation. A gap sensor 4 is arranged so as to oppose the target face 2. The gap sensor 4 is fitted to a stationary part 6. The gap sensor 4 measures a gap 8 between the target face 2 and the sensor 4. By the change of this gap 8, the axial elongation of the rotary shaft 1 is measured.
In the prior art axial elongation measuring device as mentioned above, the elongation of the rotary shaft 1 is directly measured by the gap sensor 4 relative to the stationary part 6. Therefore, in case the axial elongation of the rotary shaft 1 is large, it is necessary to measure the gap 8 over a wide range. However, measuring the gap 8 with the gap sensor 4 over the wide range often results in less accuracy.
Also, as the gap sensor 4 is provided in the axial directional space around the rotary shaft 1 where the gap 8 to be measured exists, a certain space is required in the axial direction of the rotary shaft 1 for installing the gap sensor 4.
In view of the above-mentioned problems in the prior art rotary shaft axial elongation measuring device, it is an object of the present invention to provide a rotary shaft axial elongation measuring method and a device therefor that are free from such problems as mentioned above and are able to measure axial elongation of a rotary shaft with high accuracy regardless of the amount of axial elongation.
According to the present invention, a rotary shaft axial elongation measuring method for measuring axial elongation of a rotary shaft comprises providing a reference mark and a measuring mark on a rotational surface of the rotary shaft. The measuring mark is inclined relative to an axial direction of the rotary shaft. A sensor is fixed so as to oppose the rotational surface of the rotary shaft, the sensor generating pulses upon the passing of the marks during a rotation of the rotary shaft. The axial elongation of the rotary shaft is measured from a change in an interval of the pulses generated by the sensor upon passing of the reference mark and measuring mark.
According to the axial elongation measuring method of the present invention, as the measuring mark is inclined relative to the axial direction of the rotary shaft, the circumferential directional position of the measuring mark line relative to the position of the reference mark changes according to the axial directional position thereof On the other hand, the sensor generates pulses when the reference mark and the measuring mark pass by the sensor, following the rotation of the rotary shaft, and hence if the axial directional position of the rotary shaft opposing the sensor changes due to the axial elongation of the rotary shaft, then the interval of the pulses generated by the sensor differs. Consequently, by measuring the change in the interval of the pulses generated by the sensor, the axial elongation of the rotary shaft can be measured.
In the axial elongation measuring method of the present invention, the steps are simplified such that the reference mark, and the measuring mark inclined relative to the axial direction of the rotary shaft, are provided on the rotational surface of the rotary shaft, the axial elongation of which is to be measured. The sensor is fixed so as to oppose the rotational surface of the rotary shaft for generating pulses upon the passing of the marks which follow the rotation of the rotary shaft. Hence the gap between the sensor and the rotational surface of the rotary shaft opposing the sensor does not change substantially due to the axial elongation of the rotary shaft, and the accuracy of measuring the axial elongation with the sensor is in no way reduced by the amount of axial elongation. Also, according to the method of the present invention there is no need to install a sensor and a target face, as in the prior art case, in the axial directional space around the rotary shaft, and thus no case occurs where measurement becomes impossible due to limitations in the axial directional space of the rotary shaft.
The present invention further provides a rotary shaft axial elongation measuring device for measuring axial elongation of a rotary shaft. A reference mark and a measuring mark are provided on a rotational surface of the rotary shaft. The measuring mark is inclined relative to an axial direction of the rotary shaft. A sensor is fixed so as to oppose the rotational surface of the rotary shaft, the sensor generating pulses upon the passing of the marks during rotation of the rotary shaft. A data processing part measures the axial elongation of the rotary shaft from a change in an interval of the pulses generated by the sensor upon the passing of the reference mark and measuring mark.
According to the rotary shaft axial elongation measuring device of the present invention, a device is provided that is able to measure the axial elongation of the rotary shaft based on the axial elongation measuring method of the present invention as mentioned above.
In the axial elongation measuring device of the present invention, because the axial elongation data is obtained by a fixed sensor opposing the rotational surface of the rotary shaft, the gap between the sensor and the rotational surface is constant, regardless of the amount of axial elongation of the rotary shaft. Thus measurement of the axial elongation with high accuracy can be performed.
Also, in the axial elongation measuring device of the present invention, as the sensor may be arranged with a predetermined gap being maintained between itself and the rotational surface of the rotary shaft, only a narrow space is required for measuring the axial elongation, regardless of the amount of axial elongation.
The reference mark and the measuring mark provided on the rotational surface of the rotary shaft in the axial elongation measuring device of the present invention may be two marks provided such that an interval between them in the circumferential direction of the rotary shaft differs according to the axial directional position of the rotary shaft. These two marks may be two grooves or two wire members both provided in a turned V shape.
Also, the measuring mark used in the axial elongation measuring device of the present invention may be a groove or a wire member both provided in a spiral shape on the rotational surface of the rotary shaft.
As mentioned above, the axial elongation measuring device of the present invention may be of a simple construction that is made easily and is less costly.
The sensor used in the axial elongation measuring method and device of the present invention may be an ordinary gap sensor, such as a capacitance type gap sensor or eddy current gap sensor, or may be a photoelectric sensor that generates a pulse signal upon the passing of a mark provided on the rotational surface.
According to the present invention as described above, even in the case where the rotary shaft affords no space for measuring with the conventional art, thereby making the measurement of the axial elongation impossible with the conventional art, a measuring device that can be easily installed for enabling the measurement of the axial elongation is provided.